Analysis of Structural Steel Renewal Weight in Ship Repairing

Structural steel renewal (repair/replacement) is carried out as a part of routine maintenance of a ship during its service life. Structural steel renewal is a result of the structural deficiencies beyond the limit set by the classification societies, regarding either scantling (reduction in thickness) or structural deformations (yielding, buckling, bulging, etc.), or both. Reduction in thickness of steel (mainly caused by corrosion) and distortion (mainly caused by ship motion and damage due to cargo) are due to many particular natural phenomena. Structural steel replacement cost is the highest in a ship repairing invoice for a shipowner, and it also consumes the maximum resources from a shipyard. Hence, prior information about the scope of structural steel replacement might help the shipowner with proper budget allocation and schedule to meet the financial commitment. It may also help the shipyard to prepare a realistic time and berthing plan by optimizing its resource allocation and utilization. Information related to structural steel repair (weight in kg) for 123 cargo ships of various ages, deadweight, and types were collected from a single shipyard. Structural steel repairing data were then analyzed and presented in both tabular and graphical forms to show the behavior of structural steel repair as a function of age, deadweight, type, cubic number, and gross tonnage of ships. In this article, the authors have made an attempt to identify those independent variables that influence structural steel renewal (the dependent variable) and their interrelationship. 1. Introduction Rules and regulations of classification societies (CS) and flag states require a ship to call to a shipyard for various inspections at various time intervals. Because of the rules and regulations of CS and the flag state, a ship requires carrying out various surveys at different intervals. These are the annual survey (at an interval of 12 months), the docking survey (at an average interval of 24–30 months and the ship needs to enter into a dry dock for underwater inspections), the special survey (every 5 years and the ship needs to enter into a dry dock for underwater inspections), and the intermediate survey (at an interval of 36 months after the second special survey). There are other equipment and machinery inspections according to the survey status based on the age of the individual ship. During this inspection, the classification society (represented by the CS surveyor) along with the shipowner determine and confirm the extent of structural steel renewal and the shipyard carries out the steel repair work with the satisfaction of both the CS Surveyor and the shipowner.